The histopathology characterizing Alzheimer's disease (AD) involves deposition of amyloid protein (Abeta) in brain parenchyma and cerebral vessel walls, and intraneuronal neurofibrillary tangles. In patients with hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), alpha beta is deposited predominantly in the brain vasculature, causing strokes and early death. Alphabeta is an aberrant degradation product of an amyloid precursor protein (APP), encoded by a single gene on chromosome 21). To date, mutations in the APP gene have been found only in HCHWA-D and in a few families with familial AD (FAD) of early age of onset. The mutations segregate with the disease, indicating a possible role in amyloidogenesis. HCHWA-D and FAD are good models to examine the common features of diseases involving alphabeta deposition. These features include the mechanisms of APP processing, tissue origin of the alphabeta, and the APP form or a fragment thereof that is the source of alphabeta. These systems can also be used to study the causes of the clinico-pathological differences between AD, FAD and HCHWA-D. We propose: 1: to study the APP gene expression in HCHWA-D patients - that is, to identify the mRNA forms expressed; to determine which of the APP MRNA forms harbor the mutation; and to determine the tissue distribution of the mutated and normal alleles. 2: to establish in vitro models by immortalizing cells originating from HCHWA-D patients. These cells endogenously express the mutated APP gene and may contain aberrant factor(s) yet unknown, specific to the disease. The effect of mutations found in HCHWA-D and FAP patients on APP processing will also be tested in transiently or permanently transfected tissue culture cell lines of different origin. 3; to develop an animal model by constructing transgenic mice, in order to test whether the mutations in the APP gene cause accelerated alphabeta deposition in the brain. The model may contribute to our understanding of the factors involved in the rate and site of amyloid deposition. 4: to study the contribution of specific sequences of the APP gene to prevention versus acceleration of amyloid fibril formation by analysis of the in vitro and in vivo expression of the APP gene following site-specific mutagenesis.